An analysis of three recent studies finds that heterosexual African men reduced their risk of HIV infection by half after undergoing circumcision.

While there“s still more work to be done to determine the feasibility and cost–effectiveness of circumcision, the authors of the Cochrane Library analysis say there”s “strong evidence” that the procedure will protect men from the virus that causes AIDS.

In fact, the results are so convincing that “it would now be unethical to conduct further trials ” to determine whether circumcision provides protection, said lead author Nandi Siegfried, co–director of the South African Cochrane Centre at the South African Medical Research Council.

Still, researchers do not know how circumcision could affect transmission after two years. Nor do they know whether it reduces the risk for female sex partners or for men who have sex with men.

The new analysis looks at three randomized controlled studies that took place between 2002 and 2006 in South Africa, Uganda and Kenya. In all, 11,054 men (ages 18 to 24 or 15 to 49, depending on the country) took part.

Some men in the studies underwent circumcision as part of the study, while others did not. Researchers then followed the participants for up to two years to see what happened.

The new review appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence–based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

The review authors combined the results of the studies in a meta–analysis. Overall, they found that the risk of HIV infection dropped by an estimated 50 percent in circumcised men at 12 months after the procedure, and it fell by an estimated 54 percent 21 or 24 months later.

Those are promising numbers. In fact, the study researchers stopped all of the studies early because the results made it clear that circumcision worked.

The study authors reported few side effects following circumcision. In the South African study, unlike the others, those who underwent circumcision had slightly more sexual partners over a yearlong period than those who remained uncircumcised: an average of 5.9 instead of five.

Scientists are not sure why circumcision provides protection against HIV, nor why it only helps some men.

However, it does appear that the foreskin makes it easier for the virus to enter the body by allowing infectious fluids to stick around, said Dr. Sten Vermund, director of the Institute for Global Health at Vanderbilt University School of Medicine.

The layer of tissue on the underside of the foreskin is extremely thin, just one cell thick, Vermund said. To make matters worse, sexually transmitted diseases can create inflammation under the foreskin and increase the risk of transmission, he said.

From an evolutionary perspective, Vermund said, the foreskin might no longer serve a purpose by protecting the penis from hazards like wayward tree branches.“There are no more competitive advantages to keeping your penis in a sack,” he said.

Still, the idea of circumcision makes many men queasy. Moreover, several barriers, such as cost and logistics, stand in the way of circumcising all baby boys.

“The obstacles are very daunting,” Vermund said, even though it just takes 20 minutes to teach nurses to circumcise babies.

In the Western world, some critics say circumcision is painful, unnecessary and a hindrance to sexual pleasure in adulthood.

Still, policy–makers should look at circumcision as a way to prevent HIV transmission, said lead author Siegfried.

“We do need to consider every possible prevention method for reducing the rate of infection,” Siegfried said. “This review shows us that circumcision is now a potential additional strategy in our toolbox.”

The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions.

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